1. Field of the Invention
The present invention relates to an ultraviolet absorber, 2H-1-benzopyran-2-on compound which is suited for the ultraviolet absorber, and a thermoplastic resin composition and formed article thereof which comprise said ultraviolet absorber.
2. Prior Art of the Invention
Thermoplastic resins such as polyester, polymethyl methacrylate and polyvinyl chloride have excellent mechanical strengths and are widely used for films and other formed articles in view of their chemical characteristics. For example, polyester has in recent years been used in a large amount as containers of foodstuffs such as drinks, seasonings and liquors in terms of its excellent transparency, gas barrier property, and safety and hygiene. Window-sticking films have been developed for use in buildings and cars, and polyester based films in particular have been used in order to prevent window glasses from crushing and scattering in case of impact or to cut off heat radiation from outside for saving energy in air-conditioning. Further, colored polyester films having improved design have lately been marketed in view of decorative uses and have rapidly extended demand for the adhering film of window glasses which require originality for design and high performance.
On the other hand, in the field of agriculture and horticulture, thermoplastic resin films are used, for example, for growth promotion and high volume harvesting of root vegetables and other useful plants. Films based on polymethyl methacrylate and polyvinyl chloride are applied to a covering material for mulching particularly in view of light resistance, light transmittance and strength (Japanese Laid-Open Patent SHO 53-98242).
These containers and films of thermoplastic resin, for example, polyester have very excellent barrier property for ultraviolet rays of short wavelength ranging about 320 nm or less. However, ultraviolet and visible rays of long wavelength ranging about 320 nm or more mostly pass through these containers and films.
Consequently, for example, in the case of filling a fruit juice, edible oil, liquid seasoning such as "mirin" or dressing, or liquor in a polyester container and storing for several months, although there is a difference by condition of storage and by the kind of packing of foodstuffs, it often causes gradual deterioration of content, for example, delicate change in color, taste and odor. Deterioration of the content is caused by oxygen, heat, ultraviolet rays or penetration of microorganisms. Polyester containers have relatively excellent oxygen barrier property and thus prevention of deterioration of the contents can be greatly improved even under a long period of storage by further enhancing ultraviolet barrier property. Further, ultraviolet rays have been conventionally pointed out to exert a harmful influence on skin in particular. Consequently, a human body in a room can be protected by using a widow-adhering film provided with an ultraviolet barrier effect in addition to the effect on inhibiting glass scattering and cutting off heat rays.
Further, in agriculture and horticulture, mulching culture has been known to promote growth of many useful plants and to provide harvest of high quality crops in a large amount within a short period by mulching with a transparent covering material which substantially inhibits ultraviolet transmission of at least 370 nm or less (Japanese Laid-Open Patent SHO 53-124556).
At present, the industry usually conducts addition of ultraviolet absorbers in order to cut off ultraviolet rays. However, presently known ultraviolet absorbers based on hydroquinone, salicylic acid, benzophenone and benzotriazole are generally expensive compounds and require complex procedures for addition. Many absorbers are inferior in thermal stability and lead to problems such as unfavorable coloring of the resin due to thermal decomposition of the absorbers in the course of processing and embrittlement of the resin due to acceleration of cleavage in the high molecular chain of the resin. These absorbers generally sublime with ease and result in adhesion of sublimed matter on the machinery used in the steps of mixing and processing. It is also unfavorable that these absorbers are liable to migrate into the contents in the case of using the resin for containers and packaging of foodstuffs. Resins particularly comprising polyethylene terephthalate as a principal component are injection molded at very high temperatures ranging from 280.degree. C. to 320.degree. C. Consequently, ultraviolet absorbers used for the resin must have minimum sublimation in such temperature range.
Processes have been disclosed in order to solve these problems. For example, sublimation is reduced by using ultraviolet absorbers based on naphthalenetetracarboxylic acid, or anhydride, imide or ester thereof, or naphthalenedicarboxylic acid or derivatives thereof as described in Japanese Laid-Open Patent SHO 63-225650. In another process, a uniform composition is prepared by directly adding naphthalenetetracarboxylic acid or anhydride, imide or ester thereof, or naphthalenedicarboxylic acid or derivatives thereof to a preparation vessel of polybutylene terephthalate resin, and the uniform composition is successively blended with polyethylene terephthalate resin as described in Japanese Laid-Open Patent HEI 3-20353. However, the container or film comprising the composition of Japanese Laid-Open Patent SHO 63-225650 has a strong tendency to color yellow and has not been fully satisfactory to a packaging material of colorless and transparent content such as drinks and liquor. In the preparation process of formed articles in Japanese Laid-Open Patent HEI 3-20353, yellow coloring is improved by once preparing a polybutylene terephthalate resin composition comprising ultraviolet absorbable derivatives of naphthalenetetracarboxylic acid and/or naphthalenedicarboxylic acid and successively blending the resin composition with polyethylene terephthalate resin. Consequently, preparation steps are complex and the ultraviolet barrier effect cannot be expected unless the derivatives of naphthalene tetracarboxylic acid and/or naphthalene dicarboxylic acid are directly added to the polybutylene terephthalate resin preparation vessel in order to bond these derivatives to the polymer chain. As a result, the process is not always favorable as a mass production process of resin formed articles.
U.S. Pat. Nos. 4,882,412 and 4,892,922 have proposed a process for directly adding a 2H-1-benzopyran-2-on compound having a reactive group such as hydroxy, alkoxy, acyloxy, amino or acyloxyalkylamino group on the 7-position to a preparation vessel of polyethylene terephthalate resin in order to bond the compound to the polymer chain. The polyester resin composition thus obtained causes no dissolution of the benzopyran compound into the content, has ultraviolet absorbing ability and is thus suited for use in containers and packaging films of foodstuffs.
U.S. Pat. No. 5,091,501 has proposed a new preparation process of a polyester resin composition containing a known 2H-1-benzopyran-2-on compound, which comprises integrating the preparation step of the benzopyran compound with the preparation step of polyester resin, that is, simultaneously conducting preparation of polyester resin and the benzopyran compound by directly adding o-halocinnamic acid or its ester, the raw material of the benzopyran compound, to the preparation vessel of the polyester resin.
However, the resin composition described in U.S. Pat. No. 4,882,412 cannot substantially cut off ultraviolet rays of wavelengths less than 370 nm. Light transmittance of 10% or less is observed, for example, on the light beams having a wavelengths of 250.about.351 nm or incident light having a wavelength of 250.about.371 nm, as illustrated in U.S. Pat. No. 4,882,412, Examples 98 and 99.
Consequently, in the case of filling a fruit juice, edible oil or liquor in a polyester container composed of the above resin composition, the content is inevitably deteriorated by ultraviolet rays which have transmitted the container wall. The resin compositions described in U.S. Pat. Nos. 4,882,412 and 4,892,922 show a fluorescence by irradiation of ultraviolet rays or sunlight as described, for example, in U.S. Pat. No. 4,882,412, Examples 1 and 2, and U.S. Pat. No. 4,892,922, Examples 1 and 2. Consequently, packaging materials for foodstuffs and containers for filling drinks which are prepared from the above resin composition show a fluorescence and gives unfavorable impression on the appearance.
Further, yellow coloring is shown on the resin composition obtained in U.S. Pat. Nos. 4,892,922 and 5,091,501 as described in, for example, U.S. Pat. No. 4,892,922, Example 92 and U.S. Pat. No. 5,091,501, Example 3. Consequently, desired tone cannot be obtained even though a colorant is added and the resin composition is unsuited for a material of decorative window-adhering films having ultraviolet barrier effect.